Controllable electrical resistance



1968 R. DAHLBERG 3,419,767

CONTROLLABLE ELECTRICAL RES ISTANCE Filed Dec. 8, 1966 Sheet of 2 Fig. 3

INVENTOR Reinhard Dclhlberg HEY 5M0;

ATTORNEYS Dec. 31, 1968 R. DAHLBERG CONTROLLABLE ELECTRICAL RESISTANCESheet Filed Dec. 8, 1966 Fig. 4

nvvzuron Reinhard Dahlberg ATTORNEYS 3,419,767 CONTROLLABLE ELECTRICALRESISTANCE Reinhard Dahlberg, Heilbronn-Bockingen, Germany,

assignor to Telefunken Patentverwertungsgesellschaft m.b.H., Ulm(Danube), Germany Filed Dec. 8, 1966, Ser. No. 600,105 Claims priority,application Germany, Dec. 8, 1965, T 29,965 Claims. (Cl. 317-235)ABSTRACT OF THE DISCLOSURE A controllable electrical resistance in theform of a first layer made of semiconductor or insulating material,there being an electrically conductive layer on the resistance layer andtwo thermoelectric contacts on the electrically conductive layer andforming therewith a Peltier element. A voltage is applied to thecontacts which causes those electrons that are not in thermalequilibrium with their surroundings to pass out of the one of thecontacts through the electrically conductive layer and into theresistance layer, thereby to modulate the resistance thereof.

Background of the invention As is well known, electrons can pass througha highohmic semiconductor or insulating layer which is located betweentwo conductive electrodes if the semiconductor or insulating layer issufficiently thin. A high-ohmic semiconductor or insulating layerrepresents a potential peak for the electrons, the magnitude of whichpeak is determined by the electron affinity of the electrons in thesemiconductor or insulating layer. If the high-ohmic semiconductor orinsulating layer is less than 100 A. thick, there nevertheless existsthe finite possibility for the electrons to overcome this potential peakif their thermal energy is less than the electron afiinity or workfunction. Inasmuch as the probability that the electrons overcome thepotential peak is an exponential function of the thickness of thesemiconductor or insulating layer, the specific resistance of thinsemiconductor or insulating layers varies very much with the thicknessof the layer. If a voltage is applied across a very thin semiconductoror insulating layer, i.e., a layer having a thickness of about 100 A.,the current flowing through the layer is formed, primarily, by electronswhose energy is less than their affinity in the semiconductor orinsulating layer. However, this tunnel current decreases very rapidlywith increasing thickness of the semiconductor or insulating layer andthe current that then still flows is produced only by electrons whosethermal energy is greater than the electron afiinity, that is to say, byso-called hot electrons.

It is, therefore, the object of the present invention to provide anelectrical element which operates with hot electrons and which can, forexample, be used as an active element.

Summary of the invention With the above object in view, the presentinvention resides in an electric element in the form of a controllableresistance, wherein a thin layer made of a semiconductor or insulatingmaterial carries an electrically conductive nited States Patent 03,419,767 Patented Dec. 31, 1968 "ice layer, which itself carries twothermoelectric contacts so that these contacts together with theelectrically conductive layer form a Peltier element, there beingapplied to the two contacts such a voltage that those electrons whichare not in thermal equilibrium with their surroundings pass out of oneof the contacts through the electrically conductive layer and into thethin semiconductor or insulating layer and modulate the value of itsresistance.

The invention thus resides, basically, in that an electrical resistanceis modulated by hot electrons which are not in thermal equilibrium withtheir surroundings and which are injected from a thermoelectric contactinto the resistance. The controllable electrical resistance according tothe present invention thus has a technological advantage overconventional semiconductor arrangements or semiconductor amplifiers inthat the element according to the present invention operates only withelectrons, that is to say, it is an element working with majority chargecarriers rather than minority charges carriers. Since the transient orrecovery time in the electron gas is only between 10 to 10 seconds, thearrangement according to the present invention has a very high frequencylimit.

The voltages applied to the two legs of the Peltier element arepreferably smaller than twice the Peltier voltage of the thermoelement.Besides this voltage, there is applied to the resistance, between theelectrically conductive layervia a thermoelectric contactand thecollector electrode which is arranged on the opposite side of theresistance, a voltage which is no greater than the breakdown voltage ofthe resistance.

The electric resistance which is modulated by the hot electronsconsists, preferably, of a semiconductor or insulating layer which isless than 10 A. thick, the layer preferably being more than 10 A. thick.If the resistance material is a semiconductor, the energy gap of thesemiconductor material should preferably be greater than 0.7 electronvolt. If the resistance layer is :an insulating layer, the insulatingmaterial may be an oxide, a nitride, a halide, an organic insulator or avacuum gap. The thermoelectric N-legs and P-legs of the thermoelementmay, for example, consist of n-conductive and p-conductive semiconductormaterials. The thermoelement may also be con stituted by metalliccouples.

The controllable electric resistance according to the present inventionis suited, for example, for use in integrated circuits or inmicrocircuits and for amplifying very high frequencies. Since thethermal strength increases very markedly with decreasing temperatures,the element according to the present invention can be used to advantageat the temperatures of liquid nitrogen, hydrogen or helium.

Brief description of the drawings FIGURE 1 is a sectional view of oneembodiment of a resistance according to the present invention.

FIGURE 2 is a sectional view of another embodiment of a resistanceaccording to the present invention.

FIGURE 3 is a plan view of still another embodiment of a resistanceaccording to the present invention.

FIGURE 4 is a plan view of yet another embodiment of a resistanceaccording to the present invention, showing a particular contactconfiguration.

Description of the preferred embodiments FIGURE 1 shows a controllableelectric resistance according to the present invention, the samecomprising an electrical resistance 1 made of a semiconductor materialor insulating material, a thin layer serving as the thermoelectricalP-leg 2 and two thermoelectric contacts 3 and 4, serving as the N-legs.The resistance 1 is in the form of a layer on a collector electrode 5.

The electrical resistance may be made, for example, of SiO, A1 BeO, SiC,Si, GaAs and so on. The resistance may also consist of organic layers orof a vacuum gap. The P-leg 2 of the thermoelement of FIGURE 1 consistsof a layer of p-conductive thermoelectric material, as, for example,p-Si, p-InSb, and so on. The two N- contacts 3 and 4 consist of a secondthermoelectric mate rial, as, for example, Bi, p' -Si, p -Ge, and so on.

If there is applied across the N-contact 3 and the N- contact 4, bymeans of a voltage source 6, a voltage which is smaller than twice thePeltier voltage between the N-contact 4 and the P-leg 2, hot electronswill flow, depending on the polarity of the voltage, out of the N-contact 3 or out of the N-contact 4, into the P-leg 2, from whence theyare emitted into the resistance layer 1. These hot electrons passthrough the resistance layer 1, which is between about 10 and 10 A.thick, to the opposite collector electrode 5, if, by means of a voltagesource 7, a voltage is applied, via the N-contact 3 across the P-leg 2and the collector electrode 5 and hence across the resistance layer,which voltage is no greater than the breakdown voltage of the resistancelayer 1. Those electrons which come from the thermocontact and passthrough the resistance layer to the collector electrode contribute tothe current which flows between the P-leg and the collector electrodethrough the resistance layer. If the product of the voltage across theresistance layer 1 times the current through this layer which is due tothe hot electrons is greater than the product of the voltage across theN-contact 3 and the N-contact 4 times the total current produced by thisvoltage, the circuit arrangement of FIGURE 1 represents an activefour-terminal circuit.

In the arrangement shown in FIGURE 2, the collector electrode does not,as in the case of FIGURE 1, consist of a metallic layer but of ap-semiconductor 15 which carries an insulating layer 18, preferably anoxide layer. An opening is etched out of the middle of this insulatinglayer-in a manner known in the manufacture of planar semiconductors-aresistance layer 11 and an n-conductive semiconductor layer 12 beingdeposited into this opening, the same serving as the resistance and asthe N-leg of the thermoelement. The two P-contacts 13 and 14 are metallayers and consist of a metal such as aluminum, chromium-gold, and soon. The metal layers 13 and 14 are not in direct contact with the N-leg12 which is made of n-conductive semiconductor material, but areseparated from the n-conductive material by metal layers 19 and 20 whichproduce a n -contact and which see to it that the junctions between theP- and N-legs are nonrectifying junctions. The two P-contacts extendlaterally on the insulating layer 18.

FIGURE 3 shows a multiple arrangement consisting, for example, ofthirty-five of the individual Peltier elements shown in FIGURE 2. All ofthe individual elements are arranged on a common collector electrode 25,which carries the thirty-five insulating resistances and a like numberof N-legs. Only the N-legs 22, and not the resistance layers therebelow,are illustrated in FIGURE 3. In the embodiment of FIGURE 3, all of theP-contacts 23, 24 of the individual elements are connected in series.The advantage of this arrangement is that the voltage at the input ofthe circuit as a whole can be greater than in the case of the individualelements shown in FIGURES l and 2.

FIGURE 4 shows an arrangement according to the present invention whereinthe P-contacts 33 and 34 have a comblike configuration, the prongs ofthe combs nesting within each other. Not illustrated in FIGURE 4 is theresistance layer which is below the thermoelectric N- layer 32.

It will thus be seen that, in accordance with the present invention,there is provided a controllable electrical resistance, which comprisesresistance means forming a thin first layer made of a semiconductor orinsulating material, means forming an electrically conductive secondlayer on the first layer, two thermoelectric contacts on this secondlayer and forming therewith a Peltier element, and means for applying tothe contacts a voltage which causes those electrons that are not inthermal equilibrium with their surroundings to pass out of one of thecontacts through the second layer and into the first layer, thereby tomodulate the resistance thereof.

The following are illustrative examples of thermoelectric elementsaccording to the present invention.

The element of FIGURE 1 has a resistance layer 1 which is made of SiOand has a thickness of .01 mil, a thermoelectric p-layer 2 which is madeof p+-silicon and has a thickness of .01 mil, and two N-contacts 3 and 4made of aluminium. The collector electrode 5 is made of n+-silicon andhas a thickness of 10 mils. The voltages applied by voltage sources 6and 7 are 10-100 mv. and 10-100 v., respectively.

The element of FIGURE 2 has an insulating layer 18 which is made of SiOand has a thickness of .04 mil, a resistance layer 11 which is made ofintrinsic silicon and has a thickness of .1 mil, an N-conductive layer12 which is made of n -silicon and has a thickness of .1 mil, andP-contacts 13 and 14 made of p+-silicon. The layers 19 and 20 are madeof aluminium and have a thickness of .01 mil. The voltages applied byvoltage sources 6 and 7 are mv. and 10 v., respectively.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes, andadaptations.

I claim:

1. A controllable electrical resistance, comprising in combination:

(a) resistance means forming a thin first layer made of a semiconductoror insulating material;

(b) means forming an electrically conductive second layer on said firstlayer;

(c) two thermoelectric contacts on said second layer and formingtherewith a Peltier element;

(d) means for applying across said contacts a first voltage which causesthose electrons that are not in thermal equilibrium with theirsurroundings to pass out of one of said contacts through said secondlayer and into said first layer thereby to modulate the resistancethereof.

2. A controllable electrical resistance as defined in claim 1, furthercomprising:

(e) a collector electrode arranged on that side of said first layerwhich is opposite the side on which said second layer is located.

3. A controllable electrical resistance as defined in claim 2, furthercomprising:

(f) means for applying across one of said contacts and said collectorelectrode a second voltage which is no greater than the breakdownvoltage of said first layer.

4. A controllable electrical resistance as defined in claim 1 whereinsaid first voltage is smaller than twice the Peltier voltage of theelement.

5. A controllable electrical resistance as defined in claim 1 whereinsaid first layer is made of a semiconductor material having an energygap greater than 0.7 electron volt.

6. A controllable electrical resistance as defined in claim 1, furthercomprising:

(e) a collector electrode arranged on that side of said first layerwhich is opposite the side on which said second layer is located;

(f) a third layer made of insulating material arranged on that side ofsaid collector electrode on which said first layer is located, saidthird layer having an opening within which said first and second layersare located;

(g) said contacts extending laterally beyond said opening of said thirdlayer and lying on said third layer.

7. A controllable electrical resistance as defined in claim 6 whereinsaid third layer is an oxide layer.

8. A controllable electrical resistance as defined in claim 1 whereinsaid contacts have a comblike configuration, the prongs of the combsnesting within each other.

9. A controllable electrical resistance comprising a plurality ofserially connected Peltier elements each as defined in claim 1, the samebeing arranged on a common layer constituting said first layer of eachrespective Peltier element.

10. A controllable electrical resistance as defined in claim 1 whereinsaid first layer has a thickness of between 10 and 10 A.

References Cited UNITED STATES PATENTS 3,252,013 5/1966 Stanton 317-235JOHN W. HUCKERT, Primary Examiner.

0 J. D. CRAIG, Assistant Examiner.

US. Cl. X.R.

